1. Field of the Invention
The present invention relates to a coating apparatus for coating a coating solution on a web moving in a direction continuously, more particularly to a coating apparatus used for producing a photographic film, a photographic paper, an adhesive tape, a pressure selective paper, offset spring material, a battery and the like.
2. Description Related to the Prior Art
There is a coating apparatus for coating a coating solution on a continuous web or support. The coating apparatus includes a die having a manifold and a slit. In the manifold the coating solution is spread in a lengthwise direction of the manifold. Thereafter the coating solution enters from the manifold into the slit, and is discharged from the slit in a predetermined thickness. As the coating apparatus there are a slide bead coating type, an extrusion coating type, a curtain coating type and the like. For example, a structure of the slide bead coating type is disclosed in U.S. Pat. No. 2,761,419.
In the coating apparatus, it is necessary to regulate a discharging distribution of the coating solution in a lengthwise direction of the die, so as to maintain a uniformity of a flow. As a method of such regulation, there is a central feed type in which the coating solution is supplied to the central part of the manifold. In the central feed type, a coat hanger type is used usually. However, in the central feed type, an influence of a dynamic pressure becomes large, for example, when the amount of the coating solution to be fed becomes larger or the coating solution has a low viscosity. In this case, the amount of the coating solution applied on the web becomes remarkably uneven. As described in Japanese Patent-Laid Open Publication No. 6-335633, the coating solution is fed in the manifold from a side thereof so as to make the influence of the dynamic pressure smaller and the amount of discharging the coating solution constant.
In order to feed a coating solution in the manifold, a coating apparatus is provided with a connecting pipe which connects a feed metal pipe or hose with the manifold. For example, S. F. Kistler and P. M. Schweizer describes in xe2x80x9cLiquid Film Coatingxe2x80x9d (CHAPMANandHALL, 1977) about feeding the coating solution from each of the central part and a side of the feed type. However, S. F. Kistler et al does not describe concrete shapes of the connecting pipe. The concrete shape of the connecting pipe used in the central feed type is disclosed in U.S. Pat. No. 2,761,419.
Preferably the coating solution has no temperature distribution in order to make the amount of discharging uniform. However, as the connecting pipe has a complex shape, it is difficult to keep a temperature of the connecting pipe constant. Therefore, the temperature easily varies, which causes the discharging distribution of the coating solution in the lengthwise direction to become uneven.
There are little materials explained about the side-feed type in which the feed pipe or hose is connected with the manifold. For example, Yun-Han Chang made a speech of title xe2x80x9cExperimental Observation on Entrance Flow Inside Extrusion Diesxe2x80x9d in AIChE, 1996 SPRING NATIONAL MEETING (Feb. 25-29, 1996. in New Orleans USA). However, in this speech Yun-Hang Chang considers only about the flow in a sudden enlargement that generates by connecting the manifold through the connecting pipe with the tube which has different size from the manifold. However, in the side feed type, the manifold and the feed pipe are often different in size and shape. Usually, the manifold has larger size than the feed pipe. In this case the connecting pipe has an enlarged shape, and a bent pipe is used for a space saving. Inside the bent pipe, eddies generate and a pressure distribution becomes large. Accordingly, a pressure loss in the connecting pipe becomes extremely larger, which has a large influence on the discharging distribution of the coating solution in the lengthwise direction of the slit.
An object of the present invention is to provide a coating apparatus which can keep uniformly a discharging distribution of the coating solution to apply a web in a lengthwise direction of the slit.
Another object of the present invention is to provide a coating apparatus in which the coating solution can be stably fed from a side of the manifold without stirring a flow of the coating solution.
Still another object of the present invention is to provide a connecting member for stably feeding a solution from a side of the manifold without stirring a flow of the coating solution.
In order to achieve the object and the other object, a coating apparatus having a manifold provided with an entrance opening includes a divergent connecting member for connecting the entrance opening and a feed pipe (including hose) for feeding the coating solution to the manifold. The divergent connecting member has a size satisfying 1.5xe2x89xa6(B/A)xe2x89xa65.0 and 0.8xe2x89xa6(C/B)xe2x89xa68.0, when A, B and C are an equivalent diameter of an end of the divergent connecting member for connecting the feed pipe, an equivalent diameter of an end of the divergent connecting member for connecting to the entrance opening, and a length of the enlarging part respectively.
The manifold and the divergent connecting member are connected with each other such that bottoms of them are in alignment. Further, the feed pipe is connected to the divergent connecting member from a lower side of thereof, and inclined backwards from the divergent connecting member. Furthermore, in the feed pipe a static mixer is provided close to the divergent connecting member.
According to the coating apparatus of the present invention, the coating solution is fed without a flow being stirred, and the discharging distribution of the coating solution to be discharged on a web is regulated.